I think you see from the myriad of replies that difficult children are "no one size fits all" - much more so than our typical kids.
Your children are so very young, that this is something you don't need to worry about for years! In our situation, especially when difficult child was younger, here's how it worked in our house:
1. Infractions at school were handled at school and not "reconsequenced" at home.
2. There was one exception to that rule - invading the space of someone else - translation - putting any part of his body on another - kicking, poking, etc. (part of the motivation for this was to do my best to head off any future physicality when he got older). This infraction meant everything that had an "on/off" switch was off limits for however long I felt the infraction warranted.
difficult child doesn't really, oh don't jinx this board, need that kind of punishment anymore because he's not physical like he used to be - nor does he really disobey the rules.
Additionally, part of what my difficult child deals with is social. He has a tough enough time making friends that I've never taken away social aspects of his life by grounding. Not that he has a busy social life.....
I agree with the others - what works for your difficult child is what is best. Many of our difficult children don't really understand the consequence issue. I started telling my difficult child when he was in kindergarten that he had the control over himself. It was like riding a bike. If he peddled faster, the bike would go faster - if he turned the handle bars right, the bike would go right. It's the same with life. You have the control. He probably heard me say that a thousand times - but eventually it did sink in.
Today I just say, "remember, for every action there is a reaction just like for every non-action there is a reaction - both positive and negative" He needs the reminder......
Sharon